Dean Croshaw

Department of Ecology & Evolutionary Biology
E-mail address: croshaw@email.arizona.edu
Mailing address: P.O. Box 210088, University of Arizona, Tucson, Arizona 85721-0088

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Research Interests

I am a behavioral ecologist with broad interests in mating system evolution. Generally, I use genetic techniques to understand why animals behave the way they do during interactions with the opposite sex. More specifically, I am also interested in the proximate mechanisms, behavioral and physiological, that mediate the fitness outcomes of mating interactions.

Currently, I’m working with Carlos Machado and others in his lab to assess post-mating gene expression in reproductive tissues of female Drosophila pseudoobscura. The goal is to find loci in this genome that may be involved in determining the outcome of post-mating pre-fertilization sexual interactions between male ejaculate and female organs. Not only are such genes likely to be incredibly important fitness determinants of females and their mates, but they are also prime candidates to undergo sexually antagonistic coevolution. Evolutionary arms races between the sexes are incredibly interesting because they may turn out to be very strong influences in the generation of behavioral and morphological diversity as well as reproductive isolation between closely related species.

I am also developing projects to evaluate the character and extent of post-mating reproductive isolation between two sister species, D. pseudoobscura and D. persimilis. They are morphologically indistinguishable and sympatric, but hybridization is rare in nature. Currently, we have very little information about the importance of various mechanisms that maintain them as separate species. I am keen to involve undergraduate students in projects related to this, so please email me if you’re a student at PCC or UA and would like to discuss options.

In previous work, I used microsatellite DNA loci to investigate the mating system of marbled salamanders (Ambystoma opacum) a common species of the eastern deciduous forests in the US. With my coworkers, I assessed the extent of multiple paternity in a natural population and determined that it is low compared to other salamanders species. Fewer than half of 13 clutches were sired by more than one male. We used the data to compare the performance of several of the more popular statistical techniques for using microsatellite data to estimate the number of sires that contribute to sibships.

In another study, we manipulated the sex ratio in small breeding groups to create differences in the potential for sexual selection. We then evaluated different indices used in the literature to quantify the action of sexual selection. We were also interested in which traits may be important in sexual selection, so we asked whether body size was related to mating and reproductive success. Although there was strong evidence suggesting that sexual selection may be important for males in natural populations of marbled salamanders, size clearly did not matter in our study.

We also used field enclosures to compare the performance of larval salamanders from multiple paternity and single paternity clutches. Hatchlings from multiple paternity clutches had significantly higher survival to metamorphosis than those from single paternity clutches. This observation suggests a potential fitness payoff for females that mate with multiple males in a single breeding season. The good genes hypothesis to explain the evolution of polyandrous mating (despite the fitness costs) was supported over competing hypotheses.